1. Field of the Invention
This invention relates to the art of providing membranes for use in chlor-alkali electrolysis membrane cells, and in particular, to a method of pre-treating said membranes, before their insertion into a cell, to improve the quality of said membranes.
2. Description of the Prior Art
The use of membrane-type electrolysis cells for the electrolysis of brine, producing chlorine, hydrogen, and sodium hydroxide, is well known, as for example, from U.S. Pat. No. 2,967,807. It is well known that such membrane-type cells can be made by using a sheet or film, approximately 0.1 to 0.25 millimeters (about 4 to 10 or 20 mils) thick, of a copolymer of tetrafluorethylene and sulfonylfluoride perfluorovinyl ether. Suitable materials are disclosed in U.S. Pat. No. 3,282,875, and they are sold under the trademark "NAFION". Such cells offer an attractive alternative to the customary diaphragm-type cells, using a diaphragm made of asbestos or the like, because of the health hazards posed by the manufacture and use of asbestos. It is known that such membranes have a tendency, when put into service, to swell, thereby creating water domains through which hydroxide ions are transported much more readily than sodium ions, owing to the Grotthus mechanism. We are not aware that anyone has hitherto proposed any method or practice, by means of which such swelling of the membrane may be reduced, with corresponding favorable effects upon the effective selectivity of the membranes and upon the current efficiency of the chlor-alkali membrane cells in which they are used.